U.S. Pat. No. 4,624,654 -Boyd et al assigned to the assignee of this invention and incorporated by reference, describes a line for manufacturing draw tape bags from a continuous web of thin plastic film. The continuous plastic film web is fed from a supply roll and drawn through an upstream portion of the line, including a first group of work stations, by means of a first pair of input nip rolls which are continuously rotated. The continuous plastic web is intermittently advanced away from the input nip rolls and through a second group of work stations in a downstream portion of the line by a second pair of intermittently moving nip or draw rolls. The continuous web is accumulated between the first pair of nip rolls and the downstream work stations in a dancer. Several other guide rolls are provided between the dancer and the draw rolls in order to guide the intermittently advanced plastic film web through the downstream portion of the line.
It is been found in operating a bag manufacturing line of the type described in the aforesaid U.S. Pat. No. 4,624,654 at higher cycling speeds that the intermittent advancement of the continuous plastic film web through a multiroll dancer and a multiplicity of idler rolls in the downstream portion of the line introduces widely varying tension in the film which adversely affects film tracking, leading to problems such as wrinkling, and operations such as heat sealing. These adverse effects, resulting from the introduction of varying tension in the film web, limit the maximum speed at which the web can be intermittently advanced, and thus the cycling speed of the line.